Nairobi: At least one person was killed and several others were injured on Sunday when a six-storey residential building collapsed in the Kenyan capital Nairobi, officials said.

City officials said 22 survivors had been pulled out of the rubble of the building, situated in Nairobi`s Haruma neighbourhood, but said it was unclear how many others were still trapped.

The building collapsed at around 7:00 pm (1600 GMT), sparking a major rescue operation involving scores of police, city officials and medical workers, a news agency's photographer at the scene said.

Medical workers said more than 20 people had been admitted to local hospitals.

Speaking to Capital FM radio, Nairobi county official Tom Odongo said the six floors of the building were all occupied and a seventh was under construction.

He also said the upper floors were built in quick succession, putting pressure on the lower floors, and added that the construction had not been permitted by local authorities.

"The fault lies with the developer, not the county government, because responsibility starts with the individual," Odongo insisted.

Large numbers of residents also swarmed to the site, volunteering to dig in the rubble with their bare hands, although crowds were pushed away by police as heavy lifting machinery and official rescue teams were brought in.

"I`d gone out to watch the Arsenal (football) game when the building collapsed," said Eric Ochieng, a witness and resident of the building.

"I rushed back for my wife and son, and I also pulled out two people and a child in the process."

Kenya`s KTN news channel said 20 ambulances had been put on stand-by in the area.

The collapsed building borders a primary school on one side and a maze of similar, densely populated houses on the other.